The picture below is of a heatpipe that failed when too much heat was applied,
causing the slender copper cylinder to burst wide open. Yikes!

In the real world, a computer processor would
catastrophically fail or power itself down to prevent its own demise. There
is little chance a heatsink would ever reach 300°C, and stay at 300°C
for several hours causing the heatpipes to burst like little copper
firecrackers.

Fan failures are common, but modern processors are smart enough to shut down
when temperatures exceed set safety values. There is another even more insidious
gremlin in the works of most computers however - dust. If you don't clean your
CPU heatsink every now and then, enough dust will eventually build up to block
the fins of heatsink and prevent sufficient airflow from cooling the heatsink
off even though the fan's still running.

Anyway, to get to the point,
Powerelectronics.com have an interesting article written on the topic of Heat Pipe Reliability in High-Power
Electronics. The author brings up three very crucial questions that are never dealt with by CPU heatsink manufacturers.

Do heatpipes leak over long periods of time?

Will heat pipes continue to operate at their limits for
years?

What are the limits of heatpipes?

Frostytech would add:

1) Are exposed base heatpipes so thin they're apt to rupture?

2) What happens when heatpipe wicks are damaged during manufacture (flex/bending)?

3) At what temperature does the heatpipe dry out?

4) How does the heatpipe-aluminum fin joint hold up
over many hundreds of heat/cool cycles?

"The bright side is the modules ability to run tight timings at their stock frequency. After spending a few hours with them, making sure sure I got the most out of every setting while keeping them fully stable, I was able to drop them to 7-7-7-18."

FULL STORY @ NEOSEEKER(http://www.neoseeker.com/Articles/Hardware/Reviews/ocz_ddr3_1600_intel_xmp/)